中性 B 介子至強子二體稀有衰變之分支比與電荷宇稱不對稱性測量

Measurements of Branching Fractions and CP Asymmetries in Charmless Hadronic Two-body Neutral-B Meson Decays

吳姿瑩(Tzu-Ying Wu)

指導教授 ： 張寶棣

國立臺灣大學/理學院/物理研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01235

摘要

本論文中,我們收集了 772 百萬 BB 介子對,量測 B0
介子衰變至 K+π−, π+π−, K+K−, K0K0, K0π0 的分支比
及電荷宇稱之不對稱性。藉由 KEKB 不對稱能量電子正子
對撞機在 Υ(4S) 能量下,以及日本國家高能加速器中心
B 介子工廠 Belle 偵測器所收集之資料,進行量測。除了
B0 → K+K− 的衰變未有明顯訊號,其他衰變皆以大於 6
個標準差的信心水準觀測到其衰變。我們量測到其分支比
為: B(B0 → K+π−) = (20.0 ± 0.3(統計誤差)±0.6(系統誤
差)) ×10−6, B(B0 → π+π−) = (5.0 ± 0.2 ± 0.2) ×10−6,
B(B0 → K0K0) = (1.23+0.18 ± 0.03) ×10−6,以及 B(B0 → −0.17
K0π0) = (9.6 ± 0.45 ± 0.46) ×10−6,另外 B0 → K+K− 衰 變未量測到明顯訊號,我們給予 90% 信心水準的分支比上 限 1.5 × 10−7。我們也量測到 K+π− 的電荷宇稱之不對稱性
−0.063 ± 0.014+0.003。

關鍵字

分支比 ； 電荷宇稱之不對稱性 ； KEKB ； Belle偵測器 ； B介子

並列摘要

We present the final-update on the measurements of branching
fractionsforneutralBmesondecays,B0 →K+π−,π+π−,K+K−
, K0K0, K0π0, and the measurement of the direct CP violating
partial-rateasymmetriesACP inB0 →K+π−,π+π−,K0K0,K0π0
based on a data sample of 772 × 106BB pairs collected with the
Belle detector at the KEKB energy-asymmetric e+e− collider op-
erating on the Υ(4S) resonance. The data sample is around 1.7
times larger than the sample previous reported. The correspond-
ing branching fractions are to be B(B0 → K+π−) = (20.0 ±
0.3(stat.) ± 0.6(syst.)) ×10−6, B(B0 → π+π−) = (5.0 ± 0.2 ±
0.2) ×10−6, B(B0 → K0K0) = (1.23+0.18 ± 0.03) ×10−6, and −0.17
B(B0 → K0π0) = (9.6 ± 0.45 ± 0.46) ×10−6. The correspond- ing partial-rate asymmetries are ACP (B0 → K+π−) = −0.063 ± 0.014, ACP (B0 → π+π−) = 0.364±0.090, ACP (B0 → K0K0) = −0.362 ± 0.428, and ACP (B0 → K0π0) = 0.010 ± 0.130. The ratio of partial widths Rn for B0 → K+π− and K0π0 decays is Rn = 1.05 ± 0.05 ± 0.08 consistent with the expectation of Stan- dard Model. There is no signal observed for B0 → K+K− decay, and an upper limit of 1.5 × 10−7 on the branching fraction is set at 90% confidence level.

並列關鍵字

branching fraction ； charge asymmetry ； KEKB ； Belle detector ； B meson

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